scholarly journals New Protection Scheme for Internal Fault of Multi-Microgrid

2017 ◽  
Author(s):  
Fan Zhang ◽  
Longhua Mu ◽  
Wenming Guo
Keyword(s):  
Control Strategy ◽  
Simulation Analysis ◽  
High Sensitivity ◽  
Distribution Characteristics ◽  
Distributed Generations ◽  
Protection Scheme ◽  
Fault Currents ◽  
Internal Fault ◽  
Simulation Results ◽  
Flexible Operation

Multi-microgrid has many new characteristics, such as bi-directional power flows, flexible operation modes and variable fault currents with different control strategy of inverter interfaced distributed generations (IIDGs). All these featuring aspects pose challenges to multi-microgrid protection. In this paper, current and voltage characteristics of different feeders are analyzed when fault occurs in different positions of multi-microgrid. Based on the voltage and current distribution characteristics of the line parameters, a new protection scheme for the internal fault of multi-microgrid is proposed, which takes the change of phase difference and amplitude of measured bus admittance as the criterion. This scheme with high sensitivity and reliability, has a simple principle and is easy to be adjusted. PSCAD/EMTDC is used in simulation analysis, and simulation results have verified the correctness and effectiveness of the protection scheme.

A Wavelet Based Directional Algorithm for UHVDC Line Protection

2015 ◽  
Vol 713-715 ◽  
pp. 950-953
Author(s):  
Ya Jie Li ◽  
Jian Cheng Tan ◽  
Shu Xian Zhang
Keyword(s):  
High Frequency ◽  
High Voltage Direct Current ◽  
Protection Scheme ◽  
High Impedance ◽  
Internal Fault ◽  
Current Transmission ◽  
Dc Line ◽  
Simulation Results ◽  
High Impedance Faults ◽  
Transmission Line Protection

When fault distance is greater than a certain value, attenuation of high frequency fault signal over the line is greater than what the DC line boundary is subject to. To sensitively detect a fault and improve the reliability of UHVDC (Ultra High Voltage Direct Current) transmission line protection, a new protection scheme based on wavelet based direction element is proposed, where directional element and attenuation of high frequency energy are used to identify an internal fault. Extensive simulation results show that the proposed protection scheme is able to sensitively detect high impedance faults, identify the faulty pole.

scholarly journals Implementation of Optimal Protection Coordination for Microgrids with Distributed Generations Using Quaternary Protection Scheme

2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
Author(s):  
Panida Thararak ◽  
Peerapol Jirapong
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Test System ◽  
Distributed Generations ◽  
Protection Scheme ◽  
Protection Systems ◽  
Overcurrent Relays ◽  
Operation Test ◽  
Multiple Relay ◽  
Flexible Operation

The flexible operation of microgrids, along with the availability of distributed generation (DG) units, causes a variety of changes in short-circuit current levels, magnitudes, and directions, which has undesirable effects on the operation of protection systems. Conventional protection schemes use typical directional overcurrent relays (DOCRs) with limited operating capability, unable to respond to microgrid operations in the manner of short-circuit current changes. In this paper, a quaternary protection scheme implemented with dual-directional overcurrent relays (dual-DOCR) and a protection control strategy is developed for protecting against faults in microgrids, taking into account the existence of DGs and connection and disconnection of DG units. The optimal dual-DOCRs setting and coordination are formulated as an optimization problem solved by evolutionary programming to minimize the relay operating times. The proposed protection scheme is implemented with a centralized protection control system based on the smart grid concept to increase the adaptability of the dual-DOCRs, which have multiple relay setting groups in accordance with system state changes. The simulation case studies are performed using the IEEE 14-bus test system, which is modified as a meshed microgrid operation. Test scenarios, including possible operations of microgrids, DGs availabilities, and different fault events, are analyzed and discussed. The comparative studies and simulation results show that the proposed scheme provides efficient coordination between the primary and backup relays and increases the responsibility of the protection system, which can be observed from the significant reduction in the relay operating times, resulting in the enhancement of selectivity, sensitivity, and speed of microgrid protection systems.

Simulation Analysis on Control Strategy of Launch with Two Clutches for Dry DCT

2012 ◽  
Vol 479-481 ◽  
pp. 932-936
Author(s):  
Zhen Jun Liu ◽  
Chuan Bing Ren ◽  
Lei Wang
Keyword(s):  
Control Strategy ◽  
Maximum Degree ◽  
Engine Speed ◽  
Simulation Analysis ◽  
Control Process ◽  
Coordination Control ◽  
Change Rate ◽  
Maximum Change ◽  
Simulation Results ◽  
Control Principle

Based on the control principle with a constant engine speed, the coordination control process between engine and clutches during launching was analyzed. The maximum engaging speed of clutches and the maximum change rate of throttle were calculated with the maximum degree of jerk as the limited condition, and the control strategy of launch with two clutches was established. Genetic algorithm was used to optimize the distribution coefficient of torque between two clutches. The simulation results show that the control strategy of launch with two clutches using two clutches work together and the reasonable distribution of torque could be advantageous for clutches enduring life.

A Droop Control Strategy with Impedance Compensation for Low Voltage Microgrid

2013 ◽  
Vol 441 ◽  
pp. 245-248
Author(s):  
Zhi Yong Yu ◽  
Ming Lu ◽  
Zhen Nan Wang ◽  
Yi Gong Zhang
Keyword(s):  
Control Strategy ◽  
Low Voltage ◽  
Power Sharing ◽  
Droop Control ◽  
Parallel Operation ◽  
Distributed Generations ◽  
Point Of Common Coupling ◽  
Simulation Results ◽  
Common Coupling ◽  
Virtual Impedance

With conventional droop control, parallel operation of distributed generations (DG) in microgrid would lead to unbalanced power sharing. In this paper, inherent limitation of conventional droop control is analyzed. Analysis results show that different converter output impedance and line impedance make the power sharing unbalanced. In order to weaken or eliminate impedance difference from point of common coupling (PCC) to DGs, virtual impedance is introduced. By the introduction of designed virtual impedance, a novel droop control strategy with impedance compensation is proposed in this paper. Simulation results are presented from a two converters parallel-connected microgrid, showing the effectiveness of the droop control with impedance compensation. Simulation results show that DGs with proposed approach can allocate the power equally, and work stably in grid-connected mode, island mode and progress of reconnection to grid.

Research on the Fuzzy Control for Vehicle Semi-Active Suspension

2013 ◽  
Vol 683 ◽  
pp. 716-719
Author(s):  
Xiao Ming Hu ◽  
Wan Li Li
Keyword(s):  
Fuzzy Control ◽  
Control Strategy ◽  
Simulation Analysis ◽  
Control Strategies ◽  
Active Suspension ◽  
Vehicle Body ◽  
Output Current ◽  
Simulation Results ◽  
Fuzzy Control Strategy ◽  
Magneto Rheological

The whole vehicle was divided into eight pieces for establishing the semi-active suspension vehicle mode. The different fuzzy control strategies were designed according to the vertical, heeling and pitching movement of vehicle body. The vertical, heeling and pitching comprehensive vibration of the vehicle were reduced by controlling the output current of the magneto-rheological damper. Simulation analysis was operated with the parameters of a certain type of vehicle, the simulation results show that the method using the fuzzy control strategy can well improve the vehicle riding comfortableness, and its effect is superior to the optimal control.

scholarly journals Discrimination of Transformer Inrush Currents and Internal Fault Currents Using Extended Kalman Filter Algorithm (EKF)

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6020
Author(s):  
Sunil Kumar Gunda ◽  
Venkata Samba Sesha Siva Sarma Dhanikonda
Keyword(s):  
Kalman Filter ◽  
Extended Kalman Filter ◽  
Threshold Level ◽  
Transformer Protection ◽  
Protection Scheme ◽  
Fault Currents ◽  
Internal Fault ◽  
Absolute Residual ◽  
Inrush Currents ◽  
Internal Faults

The discrimination of inrush currents and internal fault currents in transformers is an important feature of a transformer protection scheme. The harmonic current restrained feature is used in conventional differential relay protection of transformers. A literature survey shows that the discrimination between the inrush currents and internal fault currents is still an area that is open to research. In this paper, the classification of internal fault currents and magnetic inrush currents in the transformer is performed by using an extended Kalman filter (EKF) algorithm. When a transformer is energized under normal conditions, the EKF estimates the primary side winding current and, hence, the absolute residual signal (ARS) value is zero. The ARS value will not be equal to zero for internal fault and inrush phenomena conditions; hence, the EKF algorithm will be used for discriminating the internal faults and inrush faults by keeping the threshold level to the ARS value. The simulation results are compared with the theoretical analysis under various conditions. It is also observed that the detection time of internal faults decreases with the severity of the fault. The results of various test cases using the EKF algorithm are presented. This scheme provides fast protection of the transformer for severe faults.

Speed regulation control of tractors’ new dual-flow transmission system based on slip rate resistance classification

2021 ◽  
pp. 095440702110105
Author(s):  
Guang Xia ◽  
Yan Xia ◽  
Xiwen Tang ◽  
Linfeng Zhao ◽  
Baoqun Sun
Keyword(s):  
Control Strategy ◽  
Control Algorithm ◽  
Production Efficiency ◽  
Sliding Mode ◽  
Slip Rate ◽  
Speed Control ◽  
Working Environment ◽  
Vehicle Speed ◽  
Speed Change ◽  
Simulation Results

Fluctuations in operation resistance during the operating process lead to reduced efficiency in tractor production. To address this problem, the project team independently developed and designed a new type of hydraulic mechanical continuously variable transmission (HMCVT). Based on introducing the mechanical structure and transmission principle of the HMCVT system, the priority of slip rate control and vehicle speed control is determined by classifying the slip rate. In the process of vehicle speed control, the driving mode of HMCVT system suitable for the current resistance state is determined by classifying the operation resistance. The speed change rule under HMT and HST modes is formulated with the goal of the highest production efficiency, and the displacement ratio adjustment surfaces under HMT and HST modes are determined. A sliding mode control algorithm based on feedforward compensation is proposed to address the problem that the oil pressure fluctuation has influences on the adjustment accuracy of hydraulic pump displacement. The simulation results of Simulink show that this algorithm can not only accurately follow the expected signal changes, but has better tracking stability than traditional PID control algorithm. The HMCVT system and speed control strategy models were built, and simulation results show that the speed control strategy can restrict the slip rate of driving wheels within the allowable range when load or road conditions change. When the tractor speed is lower than the lower limit of the high-efficiency speed range, the speed change law formulated in this paper can improve the tractor speed faster than the traditional rule, and effectively ensure the production efficiency. The research results are of great significance for improving tractor’s adaptability to complex and changeable working environment and promoting agricultural production efficiency.

scholarly journals The Flexible Operation of Coal Power and Its Renewable Integration Potential in China

2019 ◽  
Vol 11 (16) ◽  
pp. 4424 ◽  
Author(s):  
Chunning Na ◽  
Huan Pan ◽  
Yuhong Zhu ◽  
Jiahai Yuan ◽  
Lixia Ding ◽  
...  
Keyword(s):  
Renewable Energy ◽  
Power Systems ◽  
Power System ◽  
Large Scale ◽  
Renewable Integration ◽  
Flexible Resources ◽  
Feasible Option ◽  
Coal Power ◽  
Simulation Results ◽  
Flexible Operation

At present time, China’s power systems face significant challenges in integrating large-scale renewable energy and reducing the curtailed renewable energy. In order to avoid the curtailment of renewable energy, the power systems need significant flexibility requirements in China. In regions where coal is still heavily relied upon for generating electricity, the flexible operations of coal power units will be the most feasible option to face these challenges. The study first focused on the reasons why the flexible operation of existing coal power units would potentially promote the integration of renewable energy in China and then reviewed the impacts on the performance levels of the units. A simple flexibility operation model was constructed to estimate the integration potential with the existing coal power units under several different scenarios. This study’s simulation results revealed that the existing retrofitted coal power units could provide flexibility in the promotion of the integration of renewable energy in a certain extent. However, the integration potential increment of 20% of the rated power for the coal power units was found to be lower than that of 30% of the rated power. Therefore, by considering the performance impacts of the coal power units with low performances in load operations, it was considered to not be economical for those units to operate at lower than 30% of the rated power. It was believed that once the capacity share of the renewable energy had achieved a continuously growing trend, the existing coal power units would fail to meet the flexibility requirements. Therefore, it was recommended in this study that other flexible resources should be deployed in the power systems for the purpose of reducing the curtailment of renewable energy. Furthermore, based on this study’s obtained evidence, in order to realize a power system with high proportions of renewable energy, China should strive to establish a power system with adequate flexible resources in the future.

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